Terrestrial antennas for satellite communication system

ABSTRACT

Terrestrial antennas (10A, 10B, 10C and 10D) which are capable of transmitting and receiving radio signals directly to and from satellites in low Earth orbit are disclosed. The preferred embodiment of the invention employs circularly polarized, dual-frequency printed circuit antenna elements (136) measuring only a fraction of an inch in diameter. One embodiment (10A) includes an elevation array and an azimuth array which both reside on a trapezoidal, semi-conical housing that resembles a flattened pyramid. Both the top and the curved exterior of the pyramid support circular, slotted, printed circuit patches on their surfaces which bound individual radiating antenna elements (18). Since the entire antenna is only a few inches in diameter and is less than two inches high, it can be incorporated as an integral element of a telephone (T) or can be mounted at the end of a collapsible mast (CM). Other embodiments (10B, 10C, and 10D) of the invention employ hemispherical, cylindrical, and truncated hemispherical configurations. These unique antennas permit direct communication with satellites in low Earth orbit using the 20 and 30 GHz frequency bands. The antennas (10A, 10B, 10C and 10D) and their associated circuitry are sufficiently powerful to provide dependable service virtually anywhere on land, sea or in the air.

CLAIM FOR PRIORITY

The present application is a continuation of U.S. application Ser. No.07/984,609, filed on Dec. 2, 1992, now U.S. Pat. No. 5,560,788, which isa continuation-in-part of U.S. application Ser. No. 07/790,273, filedNov. 8, 1991, now abandoned.

CROSS-REFERENCES TO RELATED PATENT APPLICATIONS

The present patent application is related to the followingcommonly-owned and commonly-assigned pending patent applications:

Satellite Communication System by Edward Fenton Tuck et al., filed onOct. 28, 1991 and assigned U.S. Ser. No. 07/783,754;

Method of Conducting a Telecommunications Business Implemented on aComputer by Edward Fenton Tuck, filed on Jun. 6, 1992 and assigned U.S.Ser. No. 07/895,295;

Switching Methods for Satellite Communication System by David PalmerPatterson and Moshe Lerner Liron, filed on Nov. 8, 1992 and assignedU.S. Ser. No. 07/790,805;

Beam Compensation Methods for Satellite Communication System by DavidPalmer Patterson and Mark Alan Sturza, filed on Nov. 8, 1992 andassigned U.S. Ser. No. 07/790,318;

Spacecraft Antennas & Beam Steering Methods for Satellite CommunicationSystem by Douglas Gene Lockie et al., filed on Oct. 28, 1992 andassigned U.S. Ser. No. 07/967,988;

Spacecraft Intersatellite Link for Satellite Communication System byDouglas Gene Lockie et al., filed on Jul. 16, 1992 and assigned U.S.Ser. No. 07/915,172; and

Spacecraft Designs for Satellite Communication System by James R. Stuartand David Palmer Patterson, filed on Aug. 18, 1992 and assigned U.S.Ser. No. 07/931,625.

The specifications of the patent applications listed above are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the field of satellite communications.More particularly, this invention provides a compact, electronicallysteerable, phased-array antenna for use with a portable, hand-heldtelephone.

BACKGROUND OF THE INVENTION

While cellular phones now offer convenient service for mobile andportable telephones that was uncommon only a decade ago, currentlyavailable cellular service is limited in scope, and is often unreliableand subject to interference and interruption. Conventional cellularsystems utilize a network of land-based antenna towers called "cellsites," which send and receive microwave signals that link customersusing mobile phones in their vehicles or hand-held portable units. Sincecell sites are only found in densely populated areas, cellular serviceis severely limited. Communication links in this network are frequentlyimpaired when a customer travels from one geographical cell to another,or when hills or buildings occlude the line-of-sight pathway of themicrowave radiation which carries the signals.

Recent attempts to overcome these shortcomings of widely-availablecellular service have met with mixed results. Elaborate and heavytransportable phone systems which include a large satellite dish forcommunication directly with geosynchronous satellites have recentlybecome commercially available. These systems are bulky, require largepower supplies, and are extremely expensive.

No single public communications network is presently capable of offeringcontinuous world-wide service to a customer using a mobile or portablephone without the use of costly and large antenna systems. Theoverwhelming majority of commercial spacecraft and transponders whichare currently operating do not generally possess the power capacity tocommunicate directly with a hand-held telephone unless it is attached toan antenna dish that measures from one to several feet in diameter. Theproblem of providing an economically viable world-wide network forvoice, data, and video which can be used by mobile and portable phoneswith antennas that are matched in practical proportion to the size ofthe phone has presented a major challenge to the communicationsbusiness. The development of an easy-to-use, hand-held telephone havingits own power supply and a practical antenna suitable for directcommunication to a satellite network would constitute a majortechnological advance and would satisfy a long felt need within theelectronics and telephone industries.

SUMMARY OF THE INVENTION

The Terrestrial Antennas disclosed and claimed in this patentapplication solve the problems encountered in previous attempts toconstruct reliable and effective hand-held telephones using built-in,practical antennas that can communicate directly with spacecraft inorbit. The present invention comprises a novel, compact, multi-element,electronically steerable phased array antenna. The various embodimentsof the invention utilize active phased array designs which use printedcircuit antenna and MMIC technology. These designs employ circularlypolarized, dual-frequency printed circuit antenna elements measuringonly a fraction of an inch in diameter. One of the embodiments of theinvention includes an elevation array and an azimuth array which bothreside on a trapezoidal, semi-conical housing that resembles a flattenedpyramid. Both the top and the curved exterior of the pyramid supportcircular, slotted, printed circuit patches on their surfaces which boundindividual radiating antenna elements. Since the entire antenna is onlya few inches in diameter and less than two inches high, it can beincorporated as an integral element of the phone or can be mounted atthe end of a retractable mast. Other embodiments of the invention employhemispherical, cylindrical and truncated hemispherical configurations.These unique antennas permit direct communication with satellites in lowEarth orbit using the 20 and 30 GHz frequency bands. The antenna and itsassociated circuitry are sufficiently powerful to provide dependableservice virtually anywhere on land, sea or in the air. The presentinvention also includes novel printed circuit low-loss delay lines thatare employed to provide required phase shifts to steer the beamsradiated by the hand-held antenna.

The present invention may be used as a vital element of a novelSatellite Communication System, which is referred to above. TheTerrestrial Antennas described and claimed in this patent applicationwill enable hand-held telephone designers to overcome the difficultieswhich plague conventional cellular phones. The present invention willoffer an entirely new class of mobile and portable communication thatwill revolutionize the telephone industry.

An appreciation of other aims and objectives of the present inventionand a more complete and comprehensive understanding of this inventionmay be achieved by studying the following description of preferredembodiments and by referring to the accompanying drawings.

A BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hand-held portable phone that includesthe present invention. In one of the preferred embodiments, ahemispherical microwave antenna extends from the body of the phone on acollapsible mast.

FIGS. 2 and 3 supply top and side views of a generally trapezoidal,semi-conical embodiment of the invention.

FIGS. 4 and 5 present top and side views of a hemispherical embodimentof the invention.

FIG. 6 is a perspective view of an embodiment of the invention whichtakes the shape of a right circular cylinder.

FIGS. 7 and 8 provide enlarged illustrations of one of the circularantenna elements. FIG. 7 is a top view and FIG. 8 is a cross-sectionalview.

FIGS. 9, 10, 11, 12 and 13 collectively furnish a schematicrepresentation of a five bit, time delay phase shifter.

FIGS. 14 and 15 are side and top views of an alternate embodiment of theinvention which incorporates dual frequency antenna elements.

FIGS. 16 and 17 are top and cross-sectional views of one of the dualfrequency antenna elements.

FIGS. 18 and 19 show enlarged side and top views of one of thealternative embodiments which incorporate the dual frequency antennas.

FIGS. 20 and 21 depict enlarged top and cross-sectional views of one ofthe dual frequency antenna elements.

FIGS. 22 and 23 reveal schematic diagrams of the receive and transmitcircuits utilized in one of the several embodiments of the invention.

FIGS. 24 and 25 depict elevational and plan views of one of theembodiments of the invention which incorporates a hexagonal lattice ofradiating elements.

FIGS. 26 and 27 show plan and sectional views of dual-frequency, stackedelement, microstrip printed circuit antennas.

FIGS. 28 and 29 show plan and sectional views of dual-frequency,co-located, interleaved, microstrip printed circuit antennas.

FIGS. 30 and 31 show cross-sectional and plan views of 20/30 GHz,61-element, electronically steerable, phased array antennasincorporating a hexagonal lattice.

FIGS. 32 and 33 reveal another alternative embodiment of the presentinvention comprising a truncated hemispherical configuration.

A DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates a hand-held portable phone that includes aTerrestrial Antenna for a Satellite Communication System. In one of thepreferred embodiments, a hemispherical millimeter wave antenna 10 isused in conjunction with a portable telephone T that includes an LCDdisplay screen L, a keypad K, and a battery pack BP. In this version ofa compact hand-held transceiver T, the antenna 10 is mounted on acollapsible mast CM, which is shown in both the extended and stowedpositions, EX and ST.

FIGS. 2 and 3 exhibit top and side views of the invention 10A, whichincorporates a generally trapezoidal housing. An inclined exteriorsurface 12 includes an upper and a lower portion 12A and 12B. Thisslanted ring 12 is attached to both a top circular surface 14 and abottom circular surface 16. Both the side and top surfaces 12 and 14provide support for a number of generally circular antenna elements 18.In FIGS. 2-6, only one of the elements 18 is shown in detail to simplifythe drawing figures. An enlarged view of the element 18 is presented inFIG. 7. The patches 18 on the side 12 of the antenna 10A form an azimutharray, while those situated on the top 14 belong to an elevation array.These elements 18 utilize a conductive patch 20 bearing a cross-slot 22that is formed from two individual perpendicular slots 22A and 22B. Inone embodiment that is designed for use with the 20 Ghz band, thediameter of the top surface 14 is 1.5 inches (3.8 cm). The side surface12 is 1.0 inch (2.5 cm) high, and the bottom surface 16 is 2.5 inches(6.4 cm) wide. The nominal gain of this embodiment is approximately 20dB. For the 30 GHz band, the diameter of the radiating patches shrink toabout seventy percent of the larger 20 GHz antenna patch. For atrapezoidal geometry where the ratio of the bottom 16 and top 14surfaces is 5/3, beams emanated by this embodiment are capable of beingsteered electronically over 360 degrees in the azimuth plane and plus orminus 60 degrees in the elevation plane. This design provides forminimum performance degradation under several multipath environments.Active and passive microwave components are located within the housingattached to a ground plane. When used in this description and in theclaims, the terms "azimuth" and "elevation" refer to the two dimensionsin which beams are steered. The elevation dimension defines an angle EAmeasured from the local horizon from zero to ninety degrees. The azimuthdimension delineates the angle AA in the plane which is tangent to thesurface of the Earth at the location of the antenna. The range of theazimuth angle is zero to three hundred and sixty degrees.

FIGS. 4 and 5 depict another embodiment of the invention 10B, whichmakes use of dual-frequency radiating elements located on the top of ahemispherical or dome-shaped surface. A hemispherical surface 24, whichis mated to a bottom circular surface 26, is covered by antenna elements18. The preferred embodiment of this configuration 10B utilizes a domehaving a diameter of about 2.5 inches (1 cm). The nominal gain of thehemispherical antenna is about 20 dB over the desired range of scanangles. The printed circuit radiating elements, along with theirintegrated phase shifters, provide beam steering over 360 degrees in theazimuth plane and plus or minus 60 degrees in the elevation plane. Themicrostrip power dividers and combiners, impedance matching networks,amplitude taper elements and feed lines can be printed on the lowersurface of the thin hemispherical surface using chemical etchingtechniques. Solid state phase shifters, along with their drivers andcontrol circuits, can be located on a separate substrate and groundplane that are housed within the hemispherical enclosure. Thehemispherical configuration furnished by this embodiment provides amicrostrip conformal antenna built on a curved surface with a radius ofcurvature as small as 1.5 inches with minimal tensile and compressivestresses. The hemispherical configuration 10B experiences the minimumstretching forces under severe aerodynamic and environmental conditions.Due to its great mechanical integrity, the hemispherical embodiment 10Bis well suited as an antenna which can be mounted on the nose of anaircraft or on other objects that travel at high speeds.

FIG. 6 shows a perspective view of an embodiment of the invention 10Cthat takes the shape of a right circular cylinder having a curvedcylindrical surface 28, a top circular surface 30, and a bottom circularsurface 32. Like the hemisphere 10B, the cylindrical antenna 10C has anominal gain of 20 dB, and offers beam steering over 360 degrees in theazimuth plane and plus or minus 70 degrees in the elevation plane. For20 GHz operation, this antenna is designed to measure three inches (7.6cm) across and one inch (2.5 cm) high. A reduction of thirty to fortypercent can be achieved if the 30 GHz frequency is utilized. Theradiating elements 18 are arranged in parallel rows centered on thelongitudinal axis of the cylinder. The elements 18 are spaced apart tomeet the sidelobe and gain requirements of the azimuth array, and tominimize beam distortion and steering irregularities. Amplitude taperingand element spacing are also selected to provide low sidelobes over widescan angles. The radiating elements 18 are electromagnetically coupledto their feed lines to provide optimum antenna performance.

FIGS. 7 and 8 supply detailed renditions of one of the circular antennaelements 18. FIG. 7 is a top view which includes a conductive patchlayer 20 that has been milled, molded, or etched so that it bears twointersecting slots 22A and 22B. The resulting cross-slot 22 comprisestwo perpendicular slots which do not have equal lengths. The dissimilarlengths insure that the radiation emitted from the antenna 10 will becircularly polarized. FIG. 8 portrays a cross-section of element 18. Acopper patch 20 that includes cross-slot 22 sits atop a nonconductivesubstrate layer 34, which resides above a ground plane layer 36. Eachconductive patch 20 is 233 mils in diameter and from 0.25 to 1.00 milthick.

FIGS. 9, 10, 11, 12 and 13 supply schematic diagrams of a five bit, timedelay phase shifter 38. Each printed circuit delay line 40, 42, 44, 46,and 48 provides the necessary phase shift depending on the line length.In one embodiment of the invention, these lines 40, 42, 44, 46, and 48provide phase shifts of 11.25, 22.50, 45.00, 90.00, and 180.00 degrees,respectively. The present invention utilizes these conductive pathwaysto select the appropriate delay for steering the antenna beams. Eachantenna element 18 is coupled to its own phase shifter 38. Theseries-resonant printed circuit patch arrays are formed by connectingrows of patches through high impedance microstrip lines. The radiatingpatch elements are excited by low-loss microstrip lines arrangedperpendicular to the resonant arrays. Each feed line will excite all theresonant arrays, forming a pencil beam in the broadside direction. Thedirection of the beam is steered by the low-loss, phase shiftingelements with solid state switches located in the feed line. The presentinvention combines the phased array section and using a common aperturebeamformer into a compact, low-loss, low-profile antenna structure.

FIGS. 14 and 15 reveal side and top views of an alternate embodiment ofthe invention 50 which incorporates a hemispherical structure 52 coveredby dual frequency antenna elements 54. FIGS. 16 and 17 show top andcross-sectional views of one of the dual frequency antennas 54. FIGS. 18and 19 show enlarged side and top views of one of the alternativeembodiments of the dual frequency antennas. The edge of lower circularsurface 53 is visible in FIG. 18. FIGS. 20 and 21 show enlarged top andcross-sectional views of one of the dual frequency antenna elements 54which includes an upper conductive layer 56, a lower conductive layer58, and two conductive vias 59 and 60. The cross-sectional view in FIG.21 also depicts a foam layer 62, a dielectric layer 64, and a groundplane layer 66. The radiating elements are printed on a high performancesubstrate. The feed networks and distribution circuits are printed onthe lower side of the substrate. The active microwave components arelocated below the dielectric substrate. The entire antenna structure issecured to the ground plate 66.

FIGS. 22 and 23 reveal schematic block diagrams of the receive andtransmit circuits 68 and 97 utilized in one of the several embodimentsof the invention. The receive circuit 68 comprises a 20 GHz printedcircuit four element subarray 70 which includes feeds 72. The feeds 72convey signals to a first radio frequency (RF) amplifier 74, a firstband pass filter (BPF) 76, a second RF amplifier 78, and a mixer 80. Themixer 80 combines the output of the second RF amplifier 78 and a source82, which, in turn, receives the output of a synthesizer 84. The outputof the mixer 80 is fed to a third RF amplifier 86 and to an intermediatefrequency (IF) band pass filter (BPF) 90, an analog-to-digital (A/D)converter 92, a digital band pass filter (DBP) 94, and a thresholddetector 96. A decoder 88 is connected to the output lead of RFamplifier 86. The transmit circuit 97 shown in FIG. 23 contains a 30 GHzprinted circuit four element subarray 98 which has feeds 100 coupled toan amplifier 102, and encoder 104, an RF source 106 and a synthesizer108.

FIGS. 24 and 25 depict side and top views of another embodiment 110 ofthe miniaturized antenna that is characterized by a top element 112,radiating elements 114, a soft substrate 115, a ground plane 116 and adummy element 117. The radiating elements 114 are arranged in ahexagonal lattice pattern and are separated by approximately 0.075inches (0.19 cm).

FIGS. 26, 27, 28 and 29 are plan and sectional views of dual frequencyantennas. FIG. 26 exhibits a top view 118 of a 30 GHz printed circuitpatch element 120 above a 20 GHz patch element 122. FIG. 27 shows thesame hardware in a cross-sectional side view 126 that reveals thesubstrate layer 124 that separates the 30 GHz and 20 GHz elements 120and 122, as well as a layer of foam 128 and a ground plane 130. FIG 28shows a series of 30 and 20 GHz patch elements 120 and 122 residingtogether on a portion of an antenna. FIGS. 28 and 29 portray analternative arrangement in which the active patches 120 and 122 aresituated on either side of the substrate 124, as opposed to havingelement 122 embedded within substrate 124 as shown in FIG. 27.

FIGS. 30 and 31 show cross-sectional and plan views of an antenna with ahexagonal lattice. FIG. 30 comprises a cross-sectional view 132 thatincludes a radome 134 covering a dummy element 135, dual frequencyprinted circuit elements 136 and 137, a microwave substrate 138, feednetworks and distribution circuits 140, active microwave components 142,and a ground plane and support structure 144. The top view 146 shown inFIG. 31 reveals an array of 20 and 30 GHz patches 136 and 137 deployedin a hexagonal lattice with the dummy element 135 at its center.

FIGS. 32 and 33 reveal side and top views of yet another embodiment 10Dof the present invention comprising a generally hemispherical surface148 coupled to a generally flat circular surface 150. The truncatedhemisperhical embodiment 10D includes a hemispherical array 152 and atop circular array 154 of dual frequency radiating elements 136. Thehemispherical array 152 is affixed to a lower substrate 156 whichresides above a ground plane 158. The top circular array 154 is coveredby a dielectric radome 160.

The truncated hemispherical surface 148 is fabricated with anappropriate radius of curvature. The dual frequency radiating elements136 are located on both the hemispherical surface 148 and on the topcircular surface 150. This arrangement of radiating elements 136provides electronic beam steering over 360 degrees in the azimuth plane,and over plus or minus 60 degrees in the elevation plane with minimumbeam distortion. The printed circuit radiating elements 136 are locatedon the upper surface of a thin high performance substrate, while thefeed lines, power dividers and combiners and impedance matching networksare located on the lower side of the thin substrate 150. The phaseshifters, drivers and control networks are located on the lowersubstrate 156 above ground plane 158. All the circuits, except theradiating elements 136, are enclosed under and below the hemisphericalsurface 148.

The radiating elements 136 are formed using photo chemical-etchingprocesses. In the preferred embodiments, the elements 136 aremanufactured with tolerances not exceeding 0.0005" to meet the requiredRF performance levels. This antenna configuration will have a corporatefeed that is capable of providing low VSWRs over all entire scan angles.The thickness of the lower substrate 156 containing the phase shifters,drivers and control networks is optimized to meet the specific RFperformance requirements of the phased array antenna. The number of bitsfor the phase shifters is selected to satisfy the required sidelobeperformance at a minimum cost and level of complexity. The protectiveradome 160 is made from a low-loss dielectric superstrate. The thicknessof the radome 160 is selected to provide the needed mechanical strengthand to maintain optimum RF performance over all desired scan angles. Theradiating elements 136 are deployed in parallel rows centered about thevertical axis of the antenna 10D. This pattern of elements 136 rowssupply the maximum gain in the azimuth plane, since a relatively largenumber of antenna elements 136 can be accommodated over thehemispherical surface 148 given its large radius of curvature. Theprinted circuit elements, microstrip feed lines, power dividers andmatching networks are formed on a low-loss, printed circuit board withone half ounce copper on both sides using a chemical etching technique.The thickness of the thin substrate 150 is selected to achieve lowsidelobes, low VSWRs and high radiation efficiency without generatinghigher order modes.

The truncated hemispherical embodiment 10D of the electronicallysteerable phased array antenna offers an extremely low-profilestructure, high mechanical integrity, unrestricted field-of-view,improved reliability and minimum fabrication cost. In one of thepreferred embodiments, the maximum diameter will be three inches and theoverall height will not exceed one and one half inches. Since thisembodiment offers a relatively large radius of curvature, a relativelylarge number of radiating elements 136 can be accommodated on thehemispherical surface 148 with minimum tensile and compressive forces.

The Terrestrial Antennas disclosed above may be used for voice or datacommunications. The portable transceiver unit T that incorporates thepresent invention 10 will provide a direct ground to satellite link(GSL) to a constellation of 840 spacecraft in low Earth orbit. Thecompact antennas 10 are designed to send and receive signals tosatellites that are within a cone having a vertical axis that pointstoward the zenith which measures 80 degrees across. The angle from theterminal to the satellite, called the "mask angle," is sufficiently wideto insure that there are always at least two satellites in theconstellation flying overhead to service portable units, but is alsohigh enough above the horizon to virtually eliminate occultation byterrain, buildings, or trees. The 40 degree mask angle also limits thepath length of the signal, protects link margins and thus reduces powerrequirements.

The constellation of spacecraft will be capable of offering continuouscoverage between 70 degrees N and 70 degrees S latitude. Every satelliteemanates 256 simultaneous beams, which are multiplexed to 4,096positions. Regions on the ground which are illuminated by the radiobeams from the satellite are called the "footprints" or "cells" thathave hexagonal outlines and measure approximately 1400 km by 1400 km.Each individual beam illuminates a ground track of 20 km by 20 km andcarries a pilot tone which identifies the source of each beam thatenables the terrestrial transceiver to initiate contact with theorbiting network. Signal processing components residing in thespacecraft are responsible for electronically steering active antennaarrays on board each satellite. Every satellite controls the assignmentof channels to terminals requesting services. When a terminal has morethan one satellite in view, the satellites monitor the signal qualityand select which one is best suited to handle the call to the terminal.Satellites measure the time delay and Doppler shift for each subscribersignal to determine the location of the ground unit within the beamfootprint. The receive beam from the ground terminal lags the transmitbeam emitted from the satellite by a fixed interval. The terminaltransmits its data to the satellite at a delay specified by thesatellite in its preceding scan. This method is used to compensate fordelay differences caused by variations in path lengths. The scan patternamong beams is coordinated to insure that all cells being scanned at oneinstant are separated by sufficient distance to eliminate interferenceand cross-talk among customers using similar hand-held equipment.

Because the satellite antennas operate at a relatively high gain, thefootprints on the ground are relatively small. The small cell sizes,combined with the rapid motion of the satellite footprint over theEarth's surface, means that a terminal remains in the same cell for onlya few seconds. To avoid the rapid handoff from satellite to satelliteevery few seconds, an innovative logical/physical cell mapping scheme isutilized. For details about this novel technique, please refer to thecopending patent application by Patterson and Sturza entitled BeamCompensation Methods for Satellite Communication System, which iscross-noted above. For optimal performance, the vertical axis of theantenna 10 should point at the zenith, but the beam steeringcapabilities of the antenna 10 can overcome the effects of using thetransceiver T at different angles, as long as the signal from theportable phone remains pointed somewhere within the mask angle. If theorientation of the antenna 10 presents a problem for the subscriber, thehand-held unit can be connected to an external antenna which is mountedat a fixed angle or which is more sensitive. The low power design of thepresent invention substantially eliminates any radiation hazards.

The number of elements 18 which are deployed on the antennas 10 isdirectly proportional to the total gain achieved by the array. Thenumber, N, for a hexagonal lattice is given by the expression: ##EQU1##where D is the aperture and λ is the wavelength at the highestfrequency. This expression indicates that about 61 elements having twoinch (5.1 cm) aperture should be used for a frequency of 30 GHz. Theappropriate phase shift, φ, that is electronically selected to steer thebeams using the various microstrip phase delay lines is determined bythe following equation: ##EQU2## where θ is the scan angle.

The design choices for the selection of materials is largely determinedby the performance requirements that are encountered using the 20 GHzand the 30 GHz frequency bands. Three commercially available materialswould be suitable for the substrates for the present invention. Theseinclude Rohacell rigid styrofoam material and Roger RT/5870 and RT/5880materials, which are both glass microfiber-reinforced PTFE compositesubstrates. While Teflon fiberglass is an extremely rigid material,which is a desirable property for the substrate, its cost is nearlytwice that of styrofoam. The dielectric constant, e_(r), for each ofthese substrates ranges from 1.35 to 2.55. Although styrofoam is theleast expensive material, it is far less rigid than either RT/5870 orRT/5880. One quarter ounce (8 grams) copper is used for the printedcircuit antenna elements. The housing enclosure can be fabricated from alightweight aluminum alloy.

Each of the embodiments disclosed above offers a low-profile structurethat is relatively easy to fabricate. The fundamental design of theseantennas is not restricted to the microwave frequencies, and may be alsobe used in phased array radar systems, direction finding systems andreconnaissance sensors.

Although the present invention has been described in detail withreference to a particular preferred embodiment, persons possessingordinary skill in the art to which this invention pertains willappreciate that various modifications and enhancements may be madewithout departing from the spirit and scope of the claims that follow.The various orbital parameters and satellite population andconfiguration statistics that have been disclosed above are intended toeducate the reader about one preferred embodiment, and are not intendedto constrain the limits of the invention or the scope of the claims. TheList of Reference Characters which follows is intended to provide thereader with a convenient means of identifying elements of the inventionin the specification and drawings. This list is not intended todelineate or narrow the scope of the claims.

    ______________________________________    LIST OF REFERENCE CHARACTERS    ______________________________________    10   Terrestrial Antennas    10A  Trapezoidal embodiment of antenna    10B  Hemispherical embodiment of antenna    10C  Cylindrical embodiment of antenna    10D  Truncated hemispherical embodiment of antenna    12   Conical surface    12A  Upper portion of conical surface    12B  Lower portion of conical surface    14   Top circular surface    16   Bottom circular surface    18   Circular antenna element    20   Conductive patch    22   Cross-slots    22A  First slot    22B  Second slot    24   Hemispherical surface    26   Bottom circular surface    28   Cylindrical surface    30   Top circular surface    32   Bottom circular surface    34   Nonconductive substrate layer    36   Ground plane layer    38   Five bit, time delay phase shifter    40   11.25 degree delay line    42   22.50 degree delay line    44   45.00 degree delay line    46   90.00 degree delay line    48   180.00 degree delay line    50   Hemispherical configuration with dual frequency antenna elements    52   Upper hemispherical surface    53   Lower circular surface    54   Dual frequency antenna element    56   Upper conductive layer    58   Lower conductive layer    59   Conductive via    60   Conductive via    62   Foam layer    64   Dielectric layer    66   Ground plane layer    68   Receive circuit    70   Printed circuit four element subarray    72   Feeds    74   First radio frequency amplifier    76   First band pass filter    78   Second radio frequency amplifier    80   Mixer    82   Source    84   Output of synthesizer    86   Third radio frequency amplifier    88   Decoder    90   Intermediate frequency band pass filter    92   Analog-to-digital converter    94   Digital band pass filter    96   Threshold detector    97   Transmit circuit    98   Printed circuit four element subarray    100  Feeds    102  Amplifier    104  Encoder    106  Radio frequency source    108  Synthesizer    110  Alternate embodiment of miniaturized antenna    112  Top element    114  Radiating element    115  Soft substrate    116  Ground plane    117  Dummy element    118  Top view    120  30 GHz printed circuit patch element    122  20 GHz patch element    124  Substrate layer    126  Cross-sectional side view    128  Foam layer    130  Ground plane    132  Cross-sectional view    134  Radome    135  Dummy element    136  Printed dual frequency printed circuit elements    137  Printed dual frequency printed circuit elements    138  Microwave substrate    140  Feed networks and distribution circuits    142  Active microwave components    144  Ground plane and support structure    146  Top view of hexagonal array of dual frequency radiating elements    148  Hemispherical surface    150  Top flat circular substrate    152  Hemispherical array of dual frequency radiating elements    154  Top circular array of dual frequency radiating elements    156  Lower substrate    158  Ground plane    160  Radome    AA   Azimuth angle    BP   Battery pack    CM   Collapsible mast    EA   Elevation angles    EX   Retractable antenna mast in fully extended position    K    Keypad    L    LCD display screen    ST   Retractable antenna mast in stowed position    T    Telephone    ______________________________________

What is claimed is:
 1. An apparatus for use with a satellitecommunication device which is capable of communicating directly with asatellite in Earth orbit comprising:an antenna surface being generallyhemispherical in shape and capable of transmitting and receiving radiobeams to and from said satellite in Earth orbit; said antenna surfacebeing capable of steering radio beams in an azimuth dimension and in anelevation dimension; and a plurality of phased-array antenna elementsdisposed along said antenna surface, said phased-array elements eachincluding upper and lower conducting surfaces separated by an insulatinglayer, said upper conducting surface being sized to operate at a firstpredetermined frequency and said lower conducting surface being sized tooperate at a second predetermined frequency different from said firstpredetermined frequency.
 2. An apparatus for use with a satellitecommunication device which is capable of communicating directly with asatellite in Earth orbit comprising:an antenna surface capable oftransmitting and receiving radio beams to and from said satellite inEarth orbit; said antenna surface being capable of steering radio beamsin an azimuth dimension and in an elevation dimension, wherein saidantenna surface comprises first and second surface portions with saidplurality of phased-array elements being disposed along said first andsecond surface portions, said first surface portion being generallyplanar and circular in shape, said second surface portion beinggenerally trapezoidal in shape; and a plurality of phased-array antennaelements disposed along said antenna surface, said phased-array elementseach including upper and lower conducting surfaces separated by aninsulating layer, said upper conducting surface being sized to operateat a first predetermined frequency and said lower conducting surfacebeing sized to operate at a second predetermined frequency differentfrom said first predetermined frequency.
 3. An apparatus for use with asatellite communication device which is capable of communicatingdirectly with a satellite in Earth orbit comprising:an antenna surfacecapable of transmitting and receiving radio beams to and from saidsatellite in Earth orbit; said antenna surface being capable of steeringradio beams in an azimuth dimension and in an elevation dimension,wherein said antenna surface comprises first and second surface portionswith said plurality of phased-array elements being disposed along saidfirst and second surface portions, said first surface portion beinggenerally planar and circular in shape, said second surface portionbeing generally cylindrical in shape; and a plurality of phased-arrayantenna elements disposed along said antenna surface, said phased-arrayelements each including upper and lower conducting surfaces separated byan insulating layer, said upper conducting surface being sized tooperate at a first predetermined frequency and said lower conductingsurface being sized to operate at a second predetermined frequecnydifferent from said first predetermined frequency.
 4. An apparatus foruse with a satellite communication device which is capable ofcommunicating directly with a satellite in Earth orbit comprising:ahousing sized to be held by a hand of a user; an antenna surface capableof transmitting and receiving radio beams to and from said satellite inEarth orbit; said antenna surface being capable of steering radio beamsin an azimuth dimension and in an elevation dimension; a plurality ofphased-array antenna elements disposed along said antenna surface, saidphased-array elements each including upper and lower conducting surfacesseparated by an insulating layer, said upper conducting surface beingsized to operate at a first predetermined frequency and said lowerconducting surface being sized to operate at a second predeterminedfrequency different from said first predetermined frequency. atransmitter within said housing and coupled to at least a first portionof said plurality of phased-array elements; a receiver within saidhousing and coupled to at least a second portion of said plurality ofphased-array elements; and a power supply supported by said housing toprovide electrical power to said transmitter and said receiver tothereby provide a hand-held portable satellite communication device. 5.The apparatus of claim 4, further including a collapsible mast having aproximal end coupled to said housing and a distal end displaced fromsaid housing along a longitudinal axis of said mast, said antennasurface being attached to said mast at said distal end.